The present invention relates to a semiconductor device and, more particularly, to techniques which are effectively applicable to a semiconductor device employing a lead frame made of a co-per-bearing metal.
Generally, a semiconductor device formed by sealing a semiconductor chip having a circuit system and a plurality electrodes formed on a circuit forming surface, i.e., a major surface, in a sealing resin package is fabricated by an assembling process using a lead frame. More specifically, a lead frame is provided which has a frame, support leads, a die pad (tab) supported by the support leads on the frame, and a plurality of leads connected by tie bars (dam bars). An Ag paste prepared by mixing an adhesive paste, such as a thermosetting epoxy resin, and Ag powder is spread over the mounting surface of the die pad of the lead frame to form an adhesive resin film. A semiconductor chip having electrodes formed on a major surface thereof is mounted on the mounting surface of the die pad coated with the adhesive resin film with a second major surface of the semiconductor chip opposite the first major surface being in contact with the adhesive resin film formed on the die pad. The adhesive resin film is hardened to fix the semiconductor chip to the die pad. The electrodes formed on the first major surface of semiconductor chip are connected electrically to the inner leads sections of the leads of the lead frame by conductive bonding wires. The semiconductor chip, the inner leads, the die pad, the support leads and the bonding wires are sealed in a resin package. Then, the outer leads are cut off the frame of the lead frame, the tie bars are cut, the outer leads are formed in predetermined shapes, and then the support leads are cut off the frame of the lead frame.
Incidentally, it is an important problem with techniques relating to a surface-mounted semiconductor device, such as a quad flatpack package (QFP), to prevent cracks in the resin package, i.e., package cracks, due to heat applied to the surface-mounted semiconductor device for a temperature cycling test, i.e., an environmental test, or heat applied to the same during reflow soldering when mounting the semiconductor device on a wiring board. There are two known principal package cracking mechanisms that cause package cracks.
A first package cracking mechanism causes package cracks due to the separation of the die pad from the resin package and the evaporation and expansion of moisture contained in the resin package by heat applied to the semiconductor device during a temperature cycling test or reflow soldering.
A second package cracking mechanism causes package cracks due to the evaporation and expansion of moisture contained in the adhesive paste by heat applied to the semiconductor device during a temperature cycling test or reflow soldering, causing the separation of the semiconductor chip from the die pad.
A technique proposed to solve such a problem, as disclosed in, for example, Japanese Patent Laid-Open No. Sho 63-204753, uses a die pad having an area smaller than that of a semiconductor chip to be mounted thereon. According to this technique, the area of contact between a die pad and a resin package is small and hence it is possible to suppress the development of package cracks due to the evaporation and expansion of moisture absorbed by the resin package. Furthermore, since the area of the adhesive paste film sandwiched between the die pad and the semiconductor chip is small, the development of package cracks due to the evaporation and expansion of moisture absorbed by the adhesive paste film can be suppressed.
Another technique proposed to solve such a problem, as disclosed in, for example, Japanese Patent Laid-Open No. Hei 8-204107, uses an X-shaped die pad (cross tab) formed by two intersecting support leads to support a semiconductor chip at only a part of the surface thereof facing the die pad. This technique also is able to suppress the development of package cracks due to the evaporation and expansion of moisture absorbed by the resin package, and the development of package cracks due to the evaporation and expansion of moisture absorbed by the adhesive paste film.
When fabricating a semiconductor device, a Fe-Ni (iron-nickel) alloy lead frame is employed. Recently, there has been a proliferation of Cu (copper) alloy lead frames. A semiconductor device employing a Cu alloy lead frame, as compared with a semiconductor device employing an Fexe2x80x94Ni alloy lead frame, exhibits an excellent heat dissipating performance and signal transmission speed. However, since the Cu alloy lead frame has a coefficient of thermal expansion greater than that of the Fexe2x80x94Ni alloy lead frame, the semiconductor chip is liable to separate from the die pad of the Cu alloy lead frame, and so the reliability of the semiconductor device employing a Cu alloy lead frame in preventing package cracks is deteriorated.
It is effective, when a Cu alloy lead frame is employed, to reduce the area of the support leads in contact with a semiconductor chip by bonding the semiconductor chip to the support leads formed in the least possible width. However, a new problem arises when the width of the support leads is reduced.
The thickness of the adhesive resin film formed on the chip support parts of the support leads decreases with the decrease of the width of the support leads. Stress induced due to the difference in coefficient of thermal expansion between the support leads and the semiconductor chip is absorbed by the adhesive resin film. The stress absorbing ability of the adhesive resin film decreases with the decrease of the thickness of the adhesive resin film. In a bonding process and a molding process in which the support leads and the semiconductor chip are heated, it is difficult to absorb the stress induced by the difference in coefficient of thermal expansion between the support leads and the semiconductor chip due to the excessively thin adhesive resin film. Consequently, the support leads and the semiconductor chip are liable to separate from each other and the semiconductor chip bonded to the support leads falls off the support leads, which reduces the yield of the semiconductor device assembling process.
Accordingly, it is an object of the present invention to provide a technique which is capable of increasing the yield of a semiconductor device assembling process.
The above and other objects and, novel features of the present invention will become apparent from the following description and the accompanying drawings.
Representative examples of the invention disclosed in the present patent application will briefly described below.
(1) A semiconductor device comprises a semiconductor chip having a plurality of electrodes formed in a first major surface thereof; a resin package sealing the semiconductor chip therein; a plurality leads electrically connected to the electrodes of the semiconductor chip and formed so as to extend inside and outside the resin package; and a support lead supporting the semiconductor chip at a part of a second major surface of the semiconductor chip opposite the first major surface; wherein the semiconductor chip is bonded to the support lead with an adhesive tape.
(2) A semiconductor device comprises a square semiconductor chip having a plurality of electrodes formed in a first major surface thereof; a square resin package sealing the semiconductor chip therein; a plurality of leads electrically connected to the electrodes of the semiconductor chip and formed so as to extend inside and outside the resin package; and a support lead supporting the semiconductor chip at a part of a second major surface of the semiconductor chip opposite the first major surface, and extending through the two opposite corners of the semiconductor chip; wherein the semiconductor chip is bonded to the support lead with an adhesive tape.
(3) A semiconductor device comprises a square semiconductor chip having a plurality of electrodes formed in a first major surface thereof; a square resin package sealing the semiconductor chip therein; a plurality leads electrically connected to the electrodes of the semiconductor chip and formed so as to extend inside and outside the resin package; and a support lead supporting the semiconductor chip at a part of a second major surface of the semiconductor chip opposite the first major surface and extending across two opposite sides of the semiconductor chip; wherein the semiconductor chip is bonded to the support lead with an adhesive tape.
(4) A semiconductor device comprises a square semiconductor chip having a plurality of electrodes formed in a first major surface thereof; a square resin package sealing the semiconductor chip therein; a plurality leads electrically connected to the electrodes of the semiconductor chip and formed so as to extend inside and outside the resin package; and a support lead supporting the semiconductor chip at a part of a second major surface of the semiconductor chip opposite the first major surface; wherein the resin package has a resin transfer part in a first corner thereof, the support lead extends from the first corner of the resin package toward a second corner of the same opposite the first corner, and the semiconductor chip is bonded to the support lead with an adhesive tape.
(5) A semiconductor device comprises a square semiconductor chip having a plurality of electrodes formed in a first major surface thereof; a square resin package sealing the semiconductor chip therein; a plurality leads electrically connected to the electrodes of the semiconductor chip and formed so as to extend inside and outside the resin package; and a support lead supporting the semiconductor chip at a part of a second major surface of the semiconductor chip opposite the first major surface; wherein the resin package has a first side provided in its middle part with a resin transfer part, the support lead extends on an imaginary line connecting the middle part of the first side of the resin package and a middle part of a second side of the same opposite the first side, and the semiconductor chip is bonded to the support lead with an adhesive tape.
According to the foregoing means, the adhesive tape can be formed in a great thickness regardless of the width of the support lead. Accordingly, the thickness of the adhesive tape can be determined according to the amount of stress that may be induced due to the difference in coefficient of thermal expansion between the support lead and the semiconductor chip. Consequently, the occurrence of a problem that the semiconductor chip falls off the support lead after the die bonding process can be suppressed, whereby the yield of a semiconductor device assembling process can be improved.